Insulation monitoring circuit and electrical system

Abstract

The invention relates to an insulation monitoring circuit (1) comprising: - a first signal source (4) which is designed to generate a first time-variable output voltage (Va) at its output, - a coupling impedance (26) which has a series circuit consisting of a coupling capacitor (27) and a coupling resistor (28) and which is electrically connected to a reference potential (8) by means of a first terminal, said first signal source (4) being connected between a positive intermediate circuit potential (Vzk+) or a negative intermediate circuit potential (Vzk-) or a mean potential (Vzkm) and a second terminal of the coupling impedance (26), - a control unit (30) which is designed to control the first signal source (4), and - a measuring device (40) which is designed to measure a voltage (Vcom) between the mean potential (Vzkm) and the reference potential (8) and carry out an insulation monitoring process on the basis of the measured voltage (Vcom).

Description

[0001] Insulation monitoring circuit and electrical system

[0002] The invention is based on the object of providing a circuit for insulation monitoring and an electrical system containing such a circuit for insulation monitoring, which provide the most reliable insulation monitoring possible.

[0003] The insulation monitoring circuit has a first signal source or voltage source which is designed to generate a first time-varying output voltage at its output.

[0004] The insulation monitoring circuit further comprises a coupling impedance or a coupling impedance component comprising a series circuit of a coupling capacitor and a coupling resistor. The coupling impedance or coupling impedance component is electrically connected to a first terminal with a reference potential, in particular PE (Protective Earth).

[0005] The first signal source is looped between a positive intermediate circuit potential, or a negative intermediate circuit potential, or a center potential that lies midway between the positive intermediate circuit potential and the negative intermediate circuit potential, and a second connection of the coupling impedance.

[0006] The insulation monitoring circuit further comprises a control unit, for example in the form of a microprocessor controller, which is designed to control the first signal source.

[0007] The insulation monitoring circuit further comprises a measuring device configured to determine or measure a voltage between the center potential and the reference potential and to perform insulation monitoring depending on the measured voltage. The voltage between the center potential and the reference potential can be measured directly or can also be determined or calculated from other measurements, for example, based on a measurement of a voltage between the positive intermediate circuit potential and the reference potential and the negative intermediate circuit potential and the reference potential.

[0008] The insulation monitoring circuit can be used, for example, for insulation monitoring or as an insulation monitor in a vehicle. In one embodiment, the insulation monitoring circuit has a second signal source or voltage source controlled by the control unit, which is designed to generate a second time-varying output voltage at its output, wherein the first signal source and the second signal source are looped in series on the output side between the positive intermediate circuit potential and the negative intermediate circuit potential, wherein the coupling impedance is looped between a connection node of the output of the first controllable signal source and the output of the second controllable signal source and the reference potential. The first and / or the second signal source can also be used to precharge the intermediate circuit.

[0009] In one embodiment, the control device controls the first signal source and / or the second signal source such that a potential difference between the positive intermediate circuit potential and the negative intermediate circuit potential and / or a potential difference between the center potential and the reference potential has a predetermined value, in particular a time-constant value.

[0010] In one embodiment, the measuring device is designed to measure a current flowing across the coupling impedance and to further perform insulation monitoring depending on the measured current.

[0011] In one embodiment, the measuring device is designed to measure the current flowing across the coupling impedance based on a voltage drop across the coupling impedance.

[0012] In one embodiment, the measuring device is designed to further calculate an impedance, in particular a resistance and a capacitance, of the effective insulation based on the first time-varying output voltage, the second time-varying output voltage and the current flowing via the coupling impedance.

[0013] In one embodiment, the control unit is designed to control the first signal source and the second signal source for insulation monitoring in such a way that a potential at the connection node of the output of the first signal source and the output of the second signal source is temporarily greater than the positive intermediate circuit potential and temporarily smaller than the negative intermediate circuit potential.

[0014] In one embodiment, the coupling capacitor is dimensioned such that it meets a normative requirement for electrical insulation, and the coupling resistor is dimensioned such that it does not meet the normative requirements for electrical insulation. The normative requirements can be defined, for example, in UN ECE R100 (Electrical Safety of Vehicles), 2018 / 858 / EC (Framework Directive for the Approval of Vehicles and Components of the EU), EN IEC 60664-1 (Insulation Coordination, Generic Standard for Equipment with a Rated Voltage up to 1,000 V AC or 1,500 V DC), and / or EN IEC 61851-1 (Charging of Electric Vehicles).

[0015] The electrical system comprises: an intermediate circuit with a positive branch carrying a positive intermediate circuit potential and a negative branch carrying a negative intermediate circuit potential, an intermediate circuit capacitor connected between the positive branch and the negative branch of the intermediate circuit, an insulation monitoring circuit as described above, and a power converter, in particular an AC / DC, DC / DC or DC / AC converter, which is fed from the intermediate circuit.

[0016] The invention is described in detail below with reference to the drawings.

[0017] This shows:

[0018] Fig. 1 shows an electrical system with a circuit for insulation monitoring according to a first embodiment,

[0019] Fig. 2 shows an electrical system with a circuit for insulation monitoring according to a second embodiment,

[0020] Fig. 3 shows an electrical system with a circuit for insulation monitoring according to a third embodiment,

[0021] Fig. 4 shows an electrical system with an insulation monitoring circuit according to a fourth embodiment, and

[0022] Fig. 5 is a circuit diagram of an example coupling impedance.

[0023] Fig. 1 shows an electrical system 300. The electrical system 300 has a circuit 1 according to the invention for insulation monitoring.

[0024] The electrical system 300 further comprises an intermediate circuit 50 with an intermediate circuit capacitor 9, which is connected between a positive branch 2 and a negative branch 3 of the intermediate circuit 50. A positive intermediate circuit potential Vzk+ is present on the positive branch 2, and a negative intermediate circuit potential Vzk- is present on the negative branch 3.

[0025] The electrical system 300 further comprises a power converter 100, for example in the form of an AC / DC, DC / DC or DC / AC converter, which is fed from the intermediate circuit 50 and has conventional semiconductor switching means 101.

[0026] The electrical system 300 is powered by an electrical energy storage device 200, for example in the form of a battery. After precharging the intermediate circuit 50, the electrical energy storage device 200 directly supplies the intermediate circuit 50, for example, by being directly electrically connected to the intermediate circuit 50. For this purpose, controllable switching means 60 and 61 are provided, which disconnect the electrical energy storage device 200 from the intermediate circuit 50 during precharging and electrically connect the electrical energy storage device 200 to the intermediate circuit 50 after precharging.

[0027] The circuit 1 for insulation monitoring comprises: a first signal source 4 supplied from a pre-charging voltage supply 6, for example in the form of a battery, which is designed to generate a first time-varying output voltage Va at its output, a coupling impedance 26 which has a series connection of a coupling capacitor 27 and a coupling resistor 28, see Fig.5, and which is electrically connected to a reference potential 8 by a first terminal, the first signal source 4 being looped on the output side between the negative intermediate circuit potential Vzk- and a second terminal of the coupling impedance 26, a control unit 30 which is designed to control the first signal source 4, and a measuring device 40 which is designed to measure a voltage Vcom between the center potential Vzkm at a node 7 and the reference potential 8 and to carry out insulation monitoring as a function of the measured voltage Vcom.

[0028] Fig. 2 shows an electrical system 300 with a circuit 1 for insulation monitoring according to a second embodiment. In the second embodiment, the first signal source 4 is looped on the output side between the positive intermediate circuit potential Vzk+ and the second terminal of the coupling impedance 26.

[0029] Fig. 3 shows an electrical system 300 with a circuit 1 for insulation monitoring according to a third embodiment. In the third embodiment, the first signal source 4 is looped on the output side between the center potential Vzkm and the second terminal of the coupling impedance 26. The center potential Vzkm is established at a connection node between two capacitors 10 with identical capacitance, which are connected in series between the positive intermediate circuit potential Vzk+ or the first branch and the negative intermediate circuit potential Vzk- or the second branch 3.

[0030] Fig. 4 shows an electrical system 300 with a circuit 1 for insulation monitoring according to a fourth embodiment. The circuit 1 for insulation monitoring has a second signal source 5 controlled by the control unit 30, which is designed to generate a second time-varying output voltage Vb at its output. The first signal source 4 and the second signal source 5 are looped in series between the positive branch 2 and the negative branch 3 on the output side. The coupling impedance 26 is looped between a connection node N1 of the output of the first controllable signal source 4 and the output of the second controllable signal source 5 and the reference potential 8.

[0031] What is common to all embodiments shown is that the control device 30 controls the first signal source 4 and / or the second signal source 5 such that the voltage between the positive intermediate circuit potential Vzk+ and the negative intermediate circuit potential Vzk- and / or the voltage Vcom between the center potential Vzkm and the reference potential 8 has a predetermined value, in particular a time-constant value.

[0032] The measuring device 40 is designed to measure the current flowing through the coupling impedance 26 and to further perform insulation monitoring depending on the measured current.

[0033] The measuring device 40 is designed to measure the current flowing through the coupling impedance 26 based on a voltage Vr dropping across the coupling resistor 27.

[0034] The measuring device 40 is designed to further calculate the impedance, in particular a resistance and a capacitance, of the effective insulation based on the first time-varying output voltage Va, the second time-varying output voltage Vb and the current flowing through the coupling impedance 26.

[0035] The control unit 30 is designed to control the first signal source 4 and the second signal source 5 for insulation monitoring in such a way that a potential at the connection node N1 of the output of the first signal source 4 and the output of the second signal source 5 is temporarily greater than the positive intermediate circuit potential Vzk+ and temporarily smaller than the negative intermediate circuit potential Vzk-,

[0036] In vehicles with a battery voltage > 60 V DC, according to UN ECE R100, an insulation monitoring circuit or insulation monitor must be installed that can reliably detect a first fault in the IT network of the HV power grid. Using the invention, both asymmetrical Vzk+ or Vzk- to GND and symmetrical insulation faults can be detected, for example, when the insulation resistances decrease evenly between Vzk+ and Vzk-. Another application for symmetrical insulation faults arises when, for example, a connector housing in the DC voltage circuit quickly fills with a conductive liquid, causing electrical contact with a vehicle chassis. Specifically for this case, the invention offers the advantage that the insulation resistances can be measured much more quickly and shutdowns can occur more quickly.

[0037] An insulation monitoring circuit, or an isolation monitoring device (IMD), combined with an automated disconnection device (ADC) enables a vehicle to implement a safe power supply (socket) or ePTO (electrical power take-off). Unlike an RCD (residual current device), this device can detect and disconnect a single fault that does not yet pose a danger to people in an IT network. This simultaneously solves the inherent problem of multiple sockets, which are only safe if all outlets of a multiple socket have their own RCD, which is impossible to control in practice.

[0038] In addition, an insulation monitor in an ePTO enables the ePTO and thus the insulation fault to be separated from the vehicle's actual traction system when an insulation fault is detected, thus ensuring that ferry operations are not affected.

[0039] An ePTO with an integrated, safe isolation monitor therefore represents a significant competitive advantage because it enables a manufacturer to market vehicles with ePTOs without incurring the risk of personal injury.

[0040] With the coupling impedance according to the invention, the coupling capacitor takes over the actual insulation function, so that the overall insulation of the vehicle is not impaired due to the coupling impedance.

[0041] According to the invention, the insulation resistance can also be measured during pre-charging of the intermediate circuit. If the two signal sources are designed to generate a voltage that is greater than the operating voltage or intermediate circuit voltage of the HV system, a measurement signal can be generated by alternately switching the two signal sources on and off during operation, and the insulation in the HV system can be monitored via voltage measurements. This allows both symmetrical and asymmetrical insulation faults to be detected even during operation.

[0042] The two signal sources 4 and 5 are designed in such a way that an optimal measurement signal is generated depending on the size of the insulation resistance or a Cy capacitance in order to ensure reliable detection of an insulation fault even in disturbed environments

[0043] The two signal sources 4 and 5 are advantageously designed so that their respective output voltages Va and Vb can be specified by the control unit 30. This allows different output voltage waveforms and amplitudes to be specified to optimize the insulation resistance measurement depending on the vehicle's insulation system. Both the frequency, the voltage rise, and the voltage amplitude used can be adjusted to achieve optimal measurement signals.

[0044] By measuring the current flowing into the coupling impedance i c (t) it is possible to calculate the insulation resistance. The following applies: where j c (t) denotes the current flowing into the coupling impedance and C y the capacitance of all connected Y capacitors.

[0045] It is advantageous to know a good starting value for the total Cy. By repeating the measurements, it is possible to verify the Cy value for plausibility, or rather, to adjust it. Typically, the Cy of a vehicle is known at the time of manufacture and does not change because these Cy are built into the individual devices as components.

[0046] The invention makes it possible to regulate the common mode voltage Vcom and thus keep it constant over a defined time interval. As long as this control is active and the voltage remains constant, the current through all Cy is zero: and the insulation resistance R iso can be determined very reliably using the measured quantities:

[0047] This enables the measurement of the coupled test current j c(t) together with the control of the common mode voltage Vcom, a calculation of the insulation resistance is performed, even if the Cy capacitance is unknown. This allows other insulation measurement methods to be verified, or these other methods can be used to verify the plausibility of this measurement. The voltage and current measurements provide several redundant measured values ​​that can be used to determine if parts of the insulation monitor fail or if individual measurements do not deliver correct results.

[0048] During pre-charging of the intermediate circuit, it is possible, for example, to carry out an initial insulation measurement when the voltage of the HV system or the intermediate circuit voltage has only reached a safe low voltage, for example < 60V, during start-up. This provides additional safety, for example during assembly of components during vehicle production, if the pre-charging is then automatically blocked.

[0049] By measuring insulation during operation of the HV system, an insulation fault on a body or trailer can be detected while driving, allowing it to be disconnected from the traction system. Likewise, an insulation fault can be detected during operation of an ePTO, triggering immediate shutdown if a hazard is suspected due to a secondary fault.

[0050] Especially with very high Cy values, as can be expected in large vehicles, the adjustable output voltage of the signal sources 4 or 5 and thus the level of the generated signal injection i c contribute to the reliable detection of insulation faults. By appropriately selecting the test voltages of the two signal sources 4 and 5, a suitable test signal can be applied to the coupling impedance 26 even at maximum operating voltage, thus allowing the insulation to be measured even during operation.

[0051] As soon as the insulation resistance R iso is known, the value of the sum of all C y by the exponential curve of the charge or discharge of the R iso and C y This value can be used both for the calculation and for the plausibility check of the C y -value can be used.

[0052] Conversely, if the sum of all C y -values ​​are known, the insulation resistance R iso about the exponential curve of the charge or discharge of the energy given by R iso and C y This value can also be used for the calculation and plausibility check of the R iS0 -value can be used.

[0053] By appropriately controlling the signal sources 4 and 5, a charge transfer process can be triggered at the coupling capacitance, from which the sum of all C y - capacities can be calculated. This transfer process is due to the compared to the C y -Capacitances much smaller coupling capacity 28 much faster, so that the measurement result is available very quickly:

[0054] The above formula allows to calculate the C y -value can also be determined from the transient response when switching between signal sources 4 and 5.

[0055] Voltage signals generated by the signal sources can be placed in a frequency range that allows for optimal filtering of the measurement signals. This allows the measurement signal to be placed in the range from 0.1 to 10 Hz, allowing the usual interference signals above 1 kHz to be filtered out by appropriate low-pass filtering of all measurement signals above 10 Hz.

[0056] According to the invention, the coupling impedance is formed by an RC series circuit. According to the invention, the output voltages of the signal sources are adjustable in amplitude, waveform, and frequency, whereby the resulting total voltage can be greater than the operating voltage. The two signal sources 4 and 5 can be switched on or off alternately or simultaneously.

[0057] By setting the voltage of the two signal sources, it is possible to control the waveform, the rise and fall times and the duration of the output voltages, while the amplitude of the output voltages remains unchanged.

[0058] The signal sources can be connected to the intermediate circuit ZK+ and ZK- either directly or via decoupling diodes or alternatively connected components.

[0059] The voltage V m The coupling impedance can be measured to check the function of the insulation measurement and thus ensure that only correct measurement results are used.

[0060] Alternatively or additionally, the voltage across the coupling capacitance, which corresponds to the integral of the current coupled through the coupling resistance, can be measured or calculated from the remaining measured values. This allows the measured values ​​to be verified for plausibility and the coupling impedance to be checked.

Claims

Patent claims 1. A circuit (1) for insulation monitoring, comprising: a first signal source (4) which is designed to generate a first time-varying output voltage (Va) at its output, a coupling impedance (26) which has a series circuit of a coupling capacitor (27) and a coupling resistor (28) and which is electrically connected to a reference potential (8) by a first terminal, wherein the first signal source (4) is looped between a positive intermediate circuit potential (Vzk+), or a negative intermediate circuit potential (Vzk-) or a center potential (Vzkm) and a second terminal of the coupling impedance (26), a control unit (30) which is designed to control the first signal source (4), and a measuring device (40) which is designed to determine a voltage (Vcom) between the center potential (Vzkm) and the reference potential (8) and to carry out insulation monitoring as a function of the determined voltage (Vcom).

2. Circuit (1) for insulation monitoring according to claim 1, characterized in that the circuit (1) has a second signal source (5) controlled by means of the control unit (30) and designed to generate a second time-varying output voltage (Vb) at its output, wherein the first signal source (4) and the second signal source (5) are looped in series on the output side between the positive intermediate circuit potential (Vzk+) and the negative intermediate circuit potential (Vzk-), wherein the coupling impedance (26) is looped between a connection node (N1) of the output of the first controllable signal source (4) and the output of the second controllable signal source (5) and the reference potential (8).

3. Circuit (1) for insulation monitoring according to claim 2, characterized in that the control device (30) controls the first signal source (4) and / or the second signal source (5) in such a way that a potential difference between the positive intermediate circuit potential (Vzk+) and the negative intermediate circuit potential (Vzk-) and / or a potential difference (Vcom) between the center potential (Vzkm) and the reference potential (8) has a predetermined value, in particular a time-constant value.

4. Circuit (1) for insulation monitoring according to one of the preceding claims, characterized in that the measuring device (40) is designed to determine a current flowing across the coupling impedance (26) and to carry out insulation monitoring further as a function of the determined current.

5. Circuit (1) for insulation monitoring according to claim 4, characterized in that the measuring device (40) is designed to determine the current flowing across the coupling impedance (26) based on a voltage drop (Vm) across the coupling impedance (26) and / or based on a voltage drop (Vr) across the coupling resistor (28).

6. Circuit (1) for insulation monitoring according to claim 4 or 5, characterized in that the measuring device (40) is designed to further calculate an impedance, in particular a resistance and a capacitance, of an effective symmetrical insulation based on the first time-varying output voltage (Va), the second time-varying output voltage (Vb) and the current flowing via the coupling impedance (26).

7. Circuit (1) for insulation monitoring according to one of claims 4 to 6, characterized in that the measuring device (40) is designed to further measure impedances between the reference potential (8) and the positive intermediate circuit potential (Vzk+) and between the reference potential (8) and the negative reference potential (VZk-) based on the first time-varying output voltage (Va), the second time-varying output voltage (Vb) and the current flowing through the coupling impedance (26) and to convert them into respective resistance values ​​and capacitance values ​​of an effective asymmetric insulation.

8. Circuit (1) for insulation monitoring according to one of claims 2 to 7, characterized in that the control unit (30) is designed to control the first signal source (4) and the second signal source (5) for insulation monitoring in such a way that a potential at the connection node (N1) of the output of the first signal source (4) and the output of the second signal source (5) is temporarily greater than the positive intermediate circuit potential (Vzk+) and temporarily smaller than the negative intermediate circuit potential (Vzk-).

9. Circuit (1) for insulation monitoring according to one of the preceding claims, characterized in that the coupling capacitor (27) is dimensioned such that it meets a normative requirement for electrical insulation, and the coupling resistor (28) is dimensioned such that it does not meet the normative requirement for electrical insulation.

10. Electrical system (300), comprising: an intermediate circuit (50) with a positive branch (2) carrying a positive intermediate circuit potential (Vzk+) and a negative branch (3) carrying a negative intermediate circuit potential (Vzk-), at least one intermediate circuit capacitor (9, 10) looped between the positive branch (2) and the negative branch (3) of the intermediate circuit (50), a circuit (1) for insulation monitoring according to one of the preceding claims, and a power converter (100), in particular an AC / DC, DC / DC or DC / AC converter, which is fed from the intermediate circuit (50).

11. Electrical system (300) according to claim 10, characterized in that the electrical system (300) is designed to switch off the power converter (100) if the insulation monitoring circuit (1) detects an insulation fault.

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